1. Field of the Invention
The present invention relates to a process for the preparation of 4-aminobut-2-enolides.
2. Description of Related Art
Certain substituted enaminocarbonyl compounds are known as insecticidally active compounds from EP 0 539 588 A1. Moreover, the International Patent Applications WO 2007/115644, WO 2007/115643 and WO 2007/115646 describe corresponding insecticidally active enaminocarbonyl compounds.
In general, enaminocarbonyl compounds are synthesized from tetronic acid and an amine according to Scheme 1 below. This procedure is described, for example, in EP 0 539 588 A1, and also in Heterocycles Vol. 27, No. 8, pages 1907 to 1923 (1988).

A disadvantage of this process is in particular that anhydrous tetronic acid is required as starting compound, the production of which is complex and cost-intensive.
For example, tetronic acid is generally prepared starting from acetoacetic ester via a bromination and subsequent hydrogenation (cf. Synthetic Communication, 11(5), pages 385 to 390 (1981)). The total yield of tetronic acid starting from acetoacetic ester is less than 40% here, which does not make the process very attractive from an industrial point of view.
CH Patent 503 722 describes a further process for the preparation of tetronic acid. In this process, 4-chloroacetoacetic ester is reacted with an aromatic amine to give 3-arylaminocrotonolactone and then the tetronic acid is released through treatment with mineral acids. The disadvantage of this process is that the isolation of the tetronic acid is only possible by means of high-vacuum sublimation, which also does not make this process very attractive from an industrial point of view.
A further process for the preparation of tetronic acid is described in EP 0 153 615 A, in which the starting material is 2,4-dichloroacetoacetic ester. This likewise multistage and complex process produces the desired compound likewise only in a moderate overall yield of 65%.
Tetrahedron Letters, No. 31, pages 2683 and 2684 (1974) describes the preparation of tetronic acid and a corresponding enaminocarbonyl compound. The synthesis described therein is given in Scheme 2 below. The starting material used here is the dimethyl ester of acetylenedicarboxylic acid.

A disadvantage of this process is the low overall yield of only 30% and also the requirement of having to use cost-intensive starting materials, for example lithium aluminium hydride (LiAlH4), as reagents.
Furthermore, a process for the preparation of enaminocarbonyl compounds starting from methyl tetronate is known from the prior art (J. Heterocyclic Chem., 21, 1753 (1984)). For this process, the starting material used is the cost-intensive ester of 4-bromo-3-methoxybut-3-enecarboxylic acid.
A further process starts from a 4-chloroacetoacetic ester, which is reacted with amines (Heterocycles, Vol. 27, No. 8, 1988, pages 1907 to 1923). The reaction to give the aminofuran is carried out in one step. Here, the amine is added with glacial acetic acid to a solution of 4-chloroacetoacetic ester in benzene and the resulting mixture is heated under reflux for several hours. The yields of 4-methylamino-2(5H)-furanone in this synthesis are only 40%.
EP 0 123 095 A discloses a process in which tetronamide is prepared from 3-amino-4-acetoxycrotonic ester. 3-Amino-4-acetoxycrotonic ester is cost-intensive and complex to prepare, and so an economic synthesis by means of this process is not possible.
A further process for the preparation of tetronic acid starting from malonic esters and chloroacetyl chloride is known from J. Chem. Soc., Perkin Trans. 1 (1972), No. 9/10, pages 1225 to 1231. This process produces the desired target compound with a yield of only 43%.
The aforementioned International Patent Application WO 2007/115644 describes the preparation of enaminocarbonyl compounds, for example of 4-[[(6-chloropyridin-3-yl)methyl](3,3-dichloro-prop-2-en-1-yl)amino]furan-2(5H)-one by reacting 4-[[(6-chloropyridin-3-yl)methyl]amino]furan-2(5H)-one with 3-bromo-1,1-dichloroprop-1-ene (cf. Preparation Example, Process 2, Example (3)). WO 2007/115644 also describes the preparation of enaminocarbonyl compounds, for example of 4-[[(6-chloropyridin-3-yl)methyl](2-fluoroethyl)amino]furan-2(5H)-one by reacting 4-[[(2-fluoroethyl)amino]furan-2(5H)-one with 2-chloro-5-chloromethylpyridine (cf. Preparation Examples, Process 3, Example (4)). The reactions are preferably carried out with hydrides of lithium or sodium. These substrates are generally cost-intensive and at the same time can only be handled with difficulty for reasons of safety.
In WO 2009/036899, which claims the priority of the European Patent Application No. 07116639, enaminocarbonyl compounds are prepared, for example, starting from 4-(methoxycarbonyl)-5-oxo-2,5-dihydrofuran-3-ol and an amine.
where                R1 is hydrogen, alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, halocycloalkyl, alkoxy, alkyloxyalkyl, halocycloalkylalkyl or arylalkyl;        Z is hydrogen, alkali metal or alkaline earth metal; and        A is pyrid-2-yl or pyrid-4-yl or is pyrid-3-yl which is optionally substituted in position 6 by fluorine, chlorine, bromine, methyl, trifluoromethyl or trifluoromethoxy, or is pyridazin-3-yl which is optionally substituted in position 6 by chlorine or methyl, or is pyrazin-3-yl or is 2-chloropyrazin-5-yl or is 1,3-thiazol-5-yl which is optionally substituted in position 2 by chlorine or methyl, or ispyrimidinyl, pyrazolyl, thiophenyl, oxazolyl, isoxazolyl, 1,2,4-oxadiazolyl, isothiazolyl, 1,2,4-triazolyl or 1,2,5-thiadiazolyl which is optionally substituted by fluorine, chlorine, bromine, cyano, nitro, C1-C4-alkyl (which is optionally substituted by fluorine and/or chlorine), C1-C3-alkylthio (which is optionally substituted by fluorine and/or chlorine), or C1-C3-alkylsulphonyl (which is optionally substituted by fluorine and/or chlorine), or is        
in which                X is halogen, alkyl or haloalkyl and        Y is halogen, alkyl, haloalkyl, haloalkoxy, azido or cyano.        